Although the remarks in this Application, apply to television microwave trucks (hereinafter called “ENG vans”), the final use and application of this patent is not to be restricted only to ENG vans, but rather is to be applied to any vehicle equipped with an extensible mast, pole or other structure.
Often, when an operator makes such an error, the extensible structure collides with an overhead obstruction such as an overhead streetlight, a tree branch, the overhanging lip of a building, etc. At the very least, there is usually significant damage to whatever equipment has been attached to the upper end of the extensible structure, and also to the extensible structure itself.
In the case of an ENG van, for example, a pneumatic mast damaged in this way can cost several tens of thousands of dollars to remove and replace. If the electronic equipment at the top of the mast (usually, in a television application, a microwave transmitter) is damaged or destroyed too, repair or replacement can cost several tens of thousands of dollars more.
Even worse is collision with an overhead obstruction such as a charged electrical power line. Most extensible structures are of metal construction, and so power from the overhead power line will travel down the structure and charge the metal body of the ENG van with a potentially lethal level of electricity. The result can be death or serious injury by electrocution of all those associated with the ENG van including the operator, any passenger in the ENG van, and any rescue worker or bystander who tries to help.
Typically, companies which outfit ENG vans, or manufacture extensible pneumatic masts, or manufacture or sell accessories for ENG vans or pneumatic masts provide the following systems:                (a) A visual warning system that senses when the ENG van's mast is extended and flashes warning lights mounted within the ENG van's cab. (It is the inventor's experience that the majority of ENG vans produced before 2001 are equipped with this system.)        (b) An electronic device that senses overhead power lines or obstructions within a user-defined radius of the extensible mast and inhibits further extension of the mast if either overhead power lines or obstructions exist. Further, if the mast has been safely extended to partial or full height, these systems can prevent if desired the ENG van operator from shifting out of “park” and driving away until the mast is fully retracted. These systems require extensive installation procedures.        (c) An alarm that requires removal of the ENG van's dashboard in order to install a sensor, which determines if the ENG van is in “park” when the operator attempts to drive away with the mast extended. If this should be the case, the system sounds an audible alarm.        (d) A sensor on the ENG van's parking brake and, if the brake is set and the mast is extended, causes the ENG van's horn to sound if the parking brake is released. Installation requires removal of the ENG van's dashboard.        
Accordingly, what is needed is a low-cost, easily installed system which sounds an audible alarm when the ENG van operator attempts to drive away with the ENG van's mast fully or partially extended; and does not inhibit the ability of the operator to drive the vehicle with the mast extended.
In consideration of procedures necessary to produce an audible alarm when the operator tries to drive an ENG van away with its mast extended, it is obvious there are three key conditions, which must be sensed and acted upon simultaneously:                Condition 1: The system must sense, and produce an electrical signal, whenever the ENG van's mast is extended;        Condition 2: The system must sense, and produce an electrical signal, whenever the ENG Van's gearshift is moved from “park” position to any other drive position; and        Condition 3: The system must sense when Conditions 1 and 2 are met and, when the vehicle's ignition switch is turned “on” sound and lock on an audible alarm, which cannot be muted until the system is reset to “safe” mode.        
It is only when Conditions 1 and 2 are met that it is appropriate to produce an audible warning signal because a potentially hazardous condition exists.
With Respect to Condition 1:
Most of the pneumatic extensible masts used in ENG vans in the United States include a proprietary sensing system which causes a warning light or lights to flash (or, alternatively, a circuit which produces an electrical signal whenever the extensible mast is extended) in the cab of an ENG van when the mast is extended and the ignition switch is turned on. This system, however, does not produce an audible alarm unless the customer orders a more complex device which not only senses mast-up but also the presence of overhead power lines, nearby obstructions, etc. This system is expensive and requires skilled and authorized installation.
With Respect to Condition 2:
Typically, the systems, which are applied to motor vehicles, are either:                (e) gear shift assemblies which accomplished shifting the vehicle's gear ratios from one ratio to another, with gear position indication an integral part of the shifter; or        (f) a visual means to indicate on the dashboard into which gear the vehicle had been shifted.        
All of (e) above went far beyond the scope of merely indicating if the gearshift lever was or was not in “park” and required extensive installation and integration into the operating system of the vehicle.
All of (f) above required extensive installation, either by removal of the vehicle's dashboard, or by device attachment directly to the vehicle's transmission by means of brackets, cables, etc.
This invention fills the void between systems, which provide only visual warnings, and expensive systems requiring extensive installations.